1. Field of the Invention
This invention relates to valves and, more particularly, to valves employing rotating stems.
2. Description of the Prior Art
The prior art is replete with various forms of valves; a number of which are directed to the resolution of the problem of maintenance and integrity of the stem seals which effect the rotating seal between the casing and valve stem.
In addition to the above noted problem area and also related thereto is the problem of providing a valve which can be readily maintained in a field environment and, more particularly, a provision of a plug valve which may be maintained without any interruption of the flow in the line with which it is associated. One of the more typical field maintenance tasks is the replacement of the stem seals and it is important that the valve continue to function at least temporarily while these seals are being replaced.
These problems have been in many cases only partially resolved by the prior art valves and the valve contemplated by the present invention introduces a number of unique and advanced features that have not been disclosed in or suggested by such prior art valve structures.
Examples of typical prior art forms of valves in this general area and other art which may relate thereto are as follows: U.S. Pat. Nos. 1,584,699; 1,671,603; 1,680,812; 2,945,668; 3,096,070; 3,115,151; 3,231,235; 3,406,707; 3,527,682 and 3,586,289.